In the production of ferrous and nonferrous metals, it is common to employ refractory lined ladles to receive the molten metal during and after the various refining stages. These ladles are recycled and normally require preheating of the refractory lining between uses. In addition, new linings require drying out as do linings which have been repaired through patching.
Early systems of ladle drying and/or preheating involve merely placing a burner head in a ladle and firing away, but such systems were inefficient and energy wasteful. Cold air preheat stations have also been utilized but again the present cost of energy makes such systems expensive and impractical to operate.
Recuperation has also been used in ladle preheat stations. One such early system is disclosed in Widekind U.S. Pat. No. 1,057,905 where a ladle is turned upside down to form a seal against the heating station. More sophisticated ladle heating systems are disclosed in U.S. Pat. Nos. 4,223,873 and 4,229,211. All of these systems which use recuperation and based on proper sealing of the lip of the ladle to the ladle heating apparatus. The problem associated with these systems is that a tight seal between the lip of the ladle and the ladle heating apparatus is necessary to define a closed system within which the recuperators operate. In practice, the seal is difficult to achieve because the lip of the ladle is normally covered with solidified chunks of metal and other types of slag which disrupt the seal and/or cause damage to the sealing surface on the ladle heating apparatus. In addition, the systems normally require high temperature recuperators such as ceramic and separately run dilution air fans to provide a coolant for the products of combustion so as to prevent overheating of the recuperators.
Finally, other sophisticated systems have been developed for ladle preheating such as that disclosed in U.S. Pat. Nos. 4,106,755 and 4,190,235, both of which require fluidized bed technology to improve fuel efficiency.